Teegarden’s star is one of the closest to our own, at only 12.5 light-years away, but you wouldn’t know it from looking at the night sky. Teegarden’s star is a dim red dwarf star - the sun is 300,000 times brighter than it - that is only 8% of the sun’s mass, so you can’t spot it without a powerful telescope. However, a star need not be bright to have planets! Earlier this year, two rocky orbs were spotted circling the tiny star.
"The two planets resemble the inner planets of our solar system," lead author Mathias Zechmeister, from the Institute for Astrophysics at the University of Göttingen, said in a June statement. "They are only slightly heavier than Earth and are located in the so-called habitable zone, where water can be present in liquid form."
These two exoplanets, known simply as Teegarden’s star b and c, were noted to be within the star’s so-called “Goldilocks zone,” where like the porridge in the fairy tale, it’s neither too hot nor too cold to support life - it’s just right. Earth is of course inside the sun’s Goldilocks zone, and Mars and Venus are on the edges of it.
Teegarden is an ultra-cool M dwarf, meaning most light it emits is infrared. The two planets circling it complete their orbits in 4.9 earth-days (Teegarden’s star b) and 11.4 days (Teegarden’s star c) respectively. 2/2#Exoplanets #Astronomy #Astrophysics #Space #Astrobiology pic.twitter.com/ubZiK68qt9
— 𝐉𝐞𝐧𝐧𝐚 ✨ (@IAmJennaMIT) June 18, 2019
But like the lifeless Mars and Venus suggest, being in the Goldilocks zone is no guarantee of supporting life. That’s why two Israeli scientists - Amri Wandel from the Hebrew University of Jerusalem and Lev Tal-Or from Tel Aviv University - decided to probe the question of Teegarden’s star’s planets deeper. Their findings have been submitted to the Astrophysical Journal Letters.
Since Teegarden’s star is dimmer than our sun, the habitable zone surrounding it is much smaller; the two exoplanets complete an orbit in only 4.9 and 11.4 Earth days’ time, respectively. Being that close to the star, they’re tidally locked, meaning that one side always faces the star, and the other sits in perpetual night.
CARMENES @CARMENES_exopl discovered two temperate Earth-mass planet candidates around Teegarden’s Star, the smallest star where researchers have so far been able to measure the weight of a planet directly
— Carmenes Exoplanets (@CARMENES_exopl) June 18, 2019
(Zechmeister et al. A&A 2019 https://t.co/0UN9WBDonX) pic.twitter.com/N704xWV3k0
That doesn’t bode well for habitability. However, the scientists note that it’s still possible the exoplanets could support liquid water, but that the atmosphere would likely be thin. Still, even a thin atmosphere would be enough to shuffle the warm and cold air from opposing sides of the exoplanet around enough to even temperatures out a bit.
Both exoplanets are roughly Earth-sized, too - itself a noteworthy discovery, since until recently astronomers were only capable of detecting much larger exoplanets.
Teegarden's Star: A nearby system with two potentially habitable worlds discovered by @CARMENES_exopl https://t.co/Uc2Yf2WkB4 #exoplanets #astrobiology pic.twitter.com/TCId0HhvAV
— Planetary HabLab (@PlanetaryHabLab) June 18, 2019
In the end, what the astronomers could gather about the two exoplanets wasn’t much, but they were able to surmise that the two exoplanets would probably be similar to Earth and Mars in temperatures, with one having surface temperatures between 0 and 50 degrees Celsius and the other being a good deal colder.
However, red dwarf stars are often flare stars, meaning they can suddenly and unpredictably emit huge solar flares, doubling in brightness in just a few minutes’ time and shooting out bursts of energy that can strip a planet of its atmosphere and douse it in radiation.
So maybe don’t start planning those vacations quite yet.
